Field of the Invention
The invention relates to an illumination system and a projection apparatus.
Description of Related Art
A projector uses a laser beam emitted by a laser source to excite a phosphor in a phosphor wheel, and the excited phosphor provides conversion beams of different colors. Conventionally, before the laser beam irradiates the phosphor wheel, the laser beam first passes through a dichroic mirror, and is then transmitted to the phosphor wheel. A function of the dichroic mirror is, for example, pervious to the light beam with a specific light wavelength range and reflects the light beam with another specific light wavelength range. When the laser beam passes through the dichroic mirror and is transmitted to the phosphor of the phosphor wheel, the phosphor is excited by the laser beam to emit the conversion beams of different wavelengths, and the conversion beams are transmitted to the dichroic mirror along a path opposite to a transmission path of the laser beam, and are reflected to other components in the projector by the dichroic mirror. An initial design concept of the dichroic mirror is to allow the wavelength corresponding to the laser beam to penetrate there through, and reflect the wavelength corresponding to the conversion beams emitted by the excited phosphor, and is not adapted to reflect the wavelength corresponding to the laser beam. Therefore, when a part of the laser beam is not reacted with the phosphor and is reflected back to the dichroic mirror by the phosphor wheel, the laser beam may directly penetrate through the dichroic mirror to transmit back to the original laser source.
In order to resolve the above problem, in a general projector, a plurality of extra optical guide elements and optical paths are configured in the phosphor wheel. The laser beam passing through the dichroic mirror may penetrate through a transparent region of the phosphor wheel, and is guided by the aforementioned optical guide elements and the corresponding optical paths, a direction of the laser beam incident to the dichroic mirror is changed after the laser beam passes through the dichroic mirror, and the above direction is different to the direction along which the original laser beam is incident to the dichroic mirror. In this way, the laser beam passing through the dichroic mirror is guided by the aforementioned optical guide elements and is again incident to and penetrates through the dichroic mirror, and is transmitted to the other components in the projector. However, by using the aforementioned optical guide elements and additionally design optical paths in the projector, the volume of the projector is relatively large, and the cost thereof is high.
Moreover, when the laser beam continuously irradiates the phosphor on the phosphor wheel, a large amount of heat is generated, which causes a phenomenon that an intensity of the conversion beam generated by the phosphor is greatly decreased along with increase of temperature, such that an image brightness of the projector is decreased along with increase of an operation time of the projector, which results in poor reliability of the projector. Moreover, in the projector using the laser light source, a speckle phenomenon is always one of important factors causing reduction of the image quality, and the speckle phenomenon causes poor image quality of the projector. Therefore, to resolve the aforementioned problems becomes an important task for related technicians of the field.
The information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Further, the information disclosed in the Background section does not mean that one or more problems to be resolved by one or more embodiments of the invention was acknowledged by a person of ordinary skill in the art.